Flexible tanks for transporting bulk products

ABSTRACT

The specification discloses a filling/discharging structure ( 10 ) for a flexitank. The structure ( 10 ) comprises a main part ( 12 ) and a nut ( 32 ). The main part comprises an externally threaded spigot ( 20 ) encircled by a disc-like flange ( 22 ). The flange and nut have concentric patterns of ribs and grooves. The grooves are designated  38, 40, 42, 44  and the ribs are on the inner face of the flange ( 22 ) and not visible in the drawing. When the nut ( 32 ) is screwed onto the spigot  20,  the ribs enter the grooves ( 38, 40, 42, 44 ) and the wall of the flexitank is gripped between the ribs and grooves. The configuration is such that the radially innermost rib and groove pair grip the tank wall most tightly and the grip on the tank wall by the rib and groove pairs outwards of the innermost rib and groove pair decreases with distance from the innermost rib and groove pair.

RELATED APPLICATION

This application claims priority under 119 to South African Patent Application No. 2007/1515, filed Feb. 21, 2007, which application is incorporated herein by reference.

FIELD OF THE INVENTION

THIS INVENTION relates to flexible tanks for transporting bulk products and to discharge/filling structures for such tanks.

BACKGROUND TO THE INVENTION

Bulk liquids are transported using what are referred to in the industry as flexitanks. A flexitank is a flexible tank constructed using sheet material, usually sheet synthetic plastics material. The flexitank is placed within an ISO shipping container which inhibits spreading of the flexitank when it is filled.

A filling/discharging structure is secured to the flexitank. This can be positioned on the upper surface of the flexitank or close to its base.

Conventionally the filling/discharging structure is secured to the flexitank by a flange which is welded to the flexitank. Alternatively there can be two flanges which are one inside the flexitank and one outside, there being bolts which pass through the wall of the flexitank and through both flanges.

A problem which occurs with current flexitanks is that the wall of the tank is compressed in the area of the filling/discharging structure and can split in this area. The resultant spillage results in loss of the flexitank's contents and can result in damage to goods in other containers.

The object of the present invention is to provide a connection between the flexitank and the filling/discharging structure which reduces the risk of the flexitank's walling failing immediately adjacent the filling / discharging structure.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided a filling/discharging structure for a flexible tank, the structure comprising an externally threaded spigot encircled by a disc-like flange, the flange having concentric ribs or concentric grooves or a mix of concentric ribs and grooves on one face thereof, and a nut which includes a bore having threads therein compatible with the threads of the spigot so that the nut can be screwed onto the spigot, the nut including a disc-like flange having concentric ribs or concentric grooves or a mix of concentric ribs and grooves on one face thereof, the pattern of ribs or grooves or ribs and grooves on the flanges being a mirror image one of the other so that when the nut is screwed onto the spigot, each rib enters a corresponding groove, the spacing between the ribs and grooves being such that sheet material between the two flanges is gripped with most force by the radially innermost rib/groove pair, the force exerted by each other rib/groove pair decreasing progressively to the outer rib/groove pair which grips the sheet material with least force.

Each of said flanges can be of frustoconical form.

According to a further aspect of the present invention there is provided a filling/discharging structure for a flexible tank, the structure having a series of concentric ribs for gripping sheet material between themselves and a backing plate, the configuration of the ribs being such that the pressure that each rib exerts on sheet material which is between itself and the backing plate increases progressively from the radially outer rib to the radially inner rib.

The backing plate can have grooves in it for receiving the ribs whereby the sheet material is, in use, deformed by each rib and forced into a respective groove.

According to another aspect of the present invention there is provided a flexible tank having a filling/discharge structure as defined above secured to the flexible walling thereof, the walling of the flexible tank been gripped by said ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 is a side elevation of a filling/discharging structure for a flexible tank of the kind known as a “flexitank”;

FIG. 2 is a front elevation of the main part of the structure of FIG. 2;

FIG. 3 is a front elevation of a nut;

FIG. 4 is a diametral section through a flange and a spigot of the main part of the structure;

FIG. 5 is a radial section through the nut; and

FIG. 6 is a section showing the way in which ribs and grooves of the flange and nut co-operate.

DETAILED DESCRIPTION OF THE DRAWINGS

The filling/discharging structure 10 shown in the drawings comprises a hollow main body 12 which is in the form of an elbow having a vertical limb 14 and a horizontal limb 16. The lower end of the vertical limb 14 is of castellated form thereby to form flow passages 18 which cannot be blocked should the walling of the flexible tank be sucked against the end of the limb 14.

The free end portion of the limb 16 is in the form of a spigot 20 which is threaded both internally and externally. The internal and external threads, designated T1 and T2 in FIG. 4, are of the same pitch and the same hand. The thread profiles can be the same or different.

A flange 22 (see particularly FIG. 4) of dished shape encircles the limb 16 between the spigot 20 and the remainder of the limb 16.

The face of the flange 22 which is adjacent the spigot 20 has thereon four protruding ribs 24, 26, 28 and 30. The ribs are concentric, and their common centre is the axis of the limb 16.

The structure 10 further comprises a nut 32 (FIGS. 1, 3 and 5) which includes a sleeve 34 and a flange 36 at one axial end of the sleeve 34. The sleeve 34 is internally threaded, the threads on the sleeve 34 being designated T3 and being compatible with the external thread T2 on the spigot 20. The flange 36 is dished and has on the outer face thereof four grooves 38, 40, 42 and 44. The grooves are concentric and their common centre lies on the centre line of the sleeve 34.

The spacing between the ribs 24, 26, 28 and 30 matches the spacing between the grooves 38, 40, 42 and 44. The flanges 22 and 36 each constitute a frustum of a cone, the conical angles being the same. Consequently when, in the absence of the wall of a flexible tank interposed between them, the nut 32 is screwed onto the spigot 20, the flanges 22 and 36 come into face-to-face contact, each rib 24, 26, 28 and 30 entering the matching groove 38, 40, 42 and 44. The flange 22 flexes slightly as the flanges are forced together.

Turning finally to FIG. 6, this shows the flange 22 and the flange 36. The inner rib 30 is a tight fit in the groove 44. The outer rib 24 fits less tightly in the groove 38 than the rib 30 fits in the groove 44. The rib and groove pair 28, 42 fit together leaving more clearance between them than between the rib and groove pair 30, 44 but less clearance than between the rib and groove pair 26, 40. The most clearance is that between the outer rib and groove pair 24, 38.

Because the flanges 22, 32 flex when the nut is tightened, it is found that to obtain the required differential grip, the rib 24 has to have a greater root to crest height than the other ribs. The height difference between, for example, the ribs 30 and 24 is such that the smaller size rib 30 grips the wall of the flexible tank tightly whereas the flexing of the flanges reduces the grip exerted on the wall of the flexible tank by the larger rib 24 to a value less than that exerted by the rib 30.

As a consequence of this arrangement, the wall of a flexible tank, shown at 46 in FIG. 6, is compressed more by the inner rib and groove pair 30, 44 than by the outer rib and groove pair 24, 38. The degree of compression increases from the inner rib and groove pair to the outer rib and groove pair. Experimental work has shown that gripping the tank wall tightly along a circular line close to the spigot 20, and less tightly along a line close to the circumferential edges of the flanges 22, 36 decreases the incidence of tank wall failure. Each rib and groove pair grips the wall of the tank more tightly than the rib and groove pair which is radially outwardly thereof. 

1. A filling/discharging structure for a flexible tank, the structure comprising an externally threaded spigot encircled by a disc-like flange, the flange having concentric ribs or concentric grooves or a mix of concentric ribs and grooves on one face thereof, and a nut which includes a bore having threads therein compatible with the threads of the spigot so that the nut can be screwed onto the spigot, the nut including a disc-like flange having concentric ribs or concentric grooves or a mix of concentric ribs and grooves on one face thereof, the pattern of ribs or grooves or ribs and grooves on the flanges being a mirror image one of the other so that when the nut is screwed onto the spigot, each rib enters a corresponding groove, the spacing between the ribs and grooves being such that sheet material between the two flanges is gripped with most force by the radially innermost rib/groove pair, the force exerted by each other rib/groove pair decreasing progressively to the outer rib/groove pair which grips the sheet material with least force.
 2. A filling and discharging structure as claimed in claim 1, wherein each of said flanges is of frustoconical form.
 3. A filling/discharging structure for a flexible tank, the structure having a series of concentric ribs for gripping sheet material between themselves and a backing plate, the configuration of the ribs being such that the pressure that each rib exerts on sheet material that is between itself and the backing plate increases progressively from the radially outer rib to the radially inner rib.
 4. A filling/discharging structure as claimed in claim 3, wherein the backing plate has grooves in it for receiving the ribs whereby the sheet material is, in use, deformed by each rib and forced into a respective groove.
 5. A flexible tank having a filling/discharging structure as claimed in claim 1 secured to the flexible walling thereof, the walling of the tank being gripped by said ribs.
 6. A flexible tank having a filling/discharging structure as claimed in claim 2 secured to the flexible walling thereof, the walling of the tank being gripped by said ribs.
 7. A flexible tank having a filling/discharging structure as claimed in claim 3 secured to the flexible walling thereof, the walling of the tank being gripped by said ribs.
 8. A flexible tank having a filling/discharging structure as claimed in claim 4 secured to the flexible walling thereof, the walling of the tank being gripped by said ribs. 